Television scanning means



Dec. 31, 1940. K. SCHLESINGER TELEVISION SCANNING MEANS Fild Aug. 4,1936 2 Sheets-Sheet 1 Fig. 2.

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Dec. 31, 1940. K. SCHLESINGER 2,227,010

I TELEVISION SCANNING MEANS Filed Aug. 4, 1936 2 Sheets-Sheet 2 PatentedDec. 31, 1940 UNITED STATES JPATJENT QFFlCE Kurt Schlesinger, Berlin,Germany, assignor, by mesne assignments, to Loewe Radio, Inc-yacorporation of New York Application August 4, 1936, Serial No. 94,129

In Germany August 6, 1935 1 Claim. (Cl. 178' 7.1)

As well known, a transmission with interlaced groups of lines is broughtabout in the case of a televisiontransmitter with Nipkow disc (seeapplication Ser. No. 36,008, filed August 13, 1935) bythe use of aperforated disc having a plurality of spirals and having its directionof rotationso arranged that the radial movement of the imagepointsoccurs in opposition to the movement of the film image projectedon to the disc. In the above-mentioned application it has then also beenproved in what manner in the case of a relative movement of this naturebetween image point and image the correct scanning with interlaced linestakes :place. t It has already been pointed out in the applicationTSer.No. 60,295, filed January 22, 1936, that a considerabledifficultyresults in this method due to the fact that the length of thearc in respect of theinner image points is smaller than that in respectof the outer image points of the spiral. Thesectional area of a spiralaperture disc is not a rectangle, but a trapezium, whilst the lightimage projected on to the disc is, generally speaking, a rectangularimage. Since these figures are not adapted to each other, the twopart-images in the method do not exactly register. As a remedy there wasset forth the production of a trapezium in optical fashion byinclination of the plane of the film and the lens.

It is not a simple matter to adjust this trapezium so accurately thatthe desired coincidence is brought about. As a remedy and for thepurpose of facilitating the adjustment there may be employed with largemeasure of success the following method in accordance with the inventionwhich consists in thatthe time spacing between each two successive linechanging impulses is varying in such a manner that an inaccuratelyprojected image may still be reproduced in exact rectangular fashion atthe receiving screen.

The novel features which I believe to be characteristic for my inventionare set forth with particularity in the appended claim. My invention,however, both as to its organization and method of operation togetherwith further objects and advantages thereof may be best understood byreference to the following description taken in connection with theaccompanying drawings, in which Fig. 1 shows an example of a distortedimage projection.

Fig. 2 the bad result in the received picture which is due to thisdistortion in the projection to the Nipkow disc, While Figs. 3 and 4show exemplary embodiments in schematic form with which remedy may beobtained.

Referring now in particular to the figures in Fig. 1 the trapezoidalsectional area of the scanning spiral 5 is represented by the. fourcorners l 2, 3, 4. This spiral is shown as a double spiral; the idea,however, may also be extended to discs having a greater number ofspirals. It is assumed that the light image projected on to the disc,due to a slight error in the optical adjustment, is not exactlycongruent with the sectional trapezium, but differs from the same asshown by the lines I, 2', 3', 4. This light image is indicated byshading. If an image of this nature is transmitted by the disc 5 and iscomposed at the receiver in such fashion that the sectional area A isdisposed over the sectional area B, there is obtained a received imageaccording to Fig. 2 The rectangular frame of the received image a, b, c,d is filled out in'such fashion by the partscreen A that the upper edgea, b of the frame properly coincides with the length of the image lineto be transmitted. Of the lowermost image line of the part-screen A,however, there are reproduced in the received image merely the points 4and 3. The image contents of 4' to 4 and of 3 to 3 fall outside of thereceived image. All vertical lines in this image incline towards theinside, i. e., to all the greater extent the more they are situatedtowards theedge of the image-in the case of the area B the position isthe reverse to that shown in Fig. 2. In this case the image angles a, I,4 and b, 2', 3 are not recorded.

The fundamental idea of the invention consists in chronologicallycorrecting in such fashion by the transmitter the initiation of theimpulses which determine the commencement of a new line at the receiverthat the images A and B coincide. This may be performed in its mostsimple form by proceeding according to the method making use ofself-synchronising image points.

In this method the image points traverse either a particularly bright ora particularly dark edge of the image. If it is desired to correct theperiods of initiation in the case of the sectional areas A and Bindependently of each other, there is employed for this purpose inaccordance with the invention a divided marginal line. Two steel knifeedges according to Fig. 3, which are freelymovable in relation to oneanother and of which each is half the height of the image, are appliedby optical reproduction at the transmission end to the edge of theimage. The meeting point between the two knife edges passes through thecentre of the image. The middle line passes through the point 8 andagrees in length with the section are of the disc. An image point whichmoves over the surface from the left to the right supplies asynchronising signal after leaving the edge 6 or 1 of the upper or lowerknife edge. These signals occur in advanced or retarded fashiondependent on the position of the edges 6 and 1. It is possible bymovement of these two edges to cause the coincidence error in Fig. 2 atthe right hand edge of the image to disappear entirely. Theoretically itagain occurs in part at the left hand edge of the image; it has beenfound in practice, however, that this error in the screen may be made sosmall by correct adjustment of the two starting edges 6 and 1 that it isless than one image element. A condition for this is that thepreliminary adjustment of the trapezium is made to be correct so far aspossible.

Figure 4 shows still further the manner in.

which the invention may be practiced when the line synchronizingimpulses are generated by means of a light margin projected upon oneradial edge of the scanning disc 5.

. In order to obtain the synchronizing impulses at exactly equalintervals it is necessary toadjust this diaphragm ring exactly as shownschematically by the arrows in Fig. 4, a condition not easilyaccomplished in the case of double spiral scanning systems having largeradial dimensions. Referring now more particularly to Fig. 4 of thedrawings, 5 represents, as in Fig. l, the Nipkow disc having a spiral oftwo turns of apertures I and 2., The arrow indicates the direction ofrotation of the disc and accordingly the projection of the image movesupward. The part image areas belonging to the two separate spiral turnsare designated B and A as in Fig. 1 and such image areas may berectangular or trapezoidal. The designation ll represents, as also doesthe legend, the radial light margin causing the synchronization signals.According to the invention the left edge margin of the field is definedby two diaphragm elements 6 and I which may be adjusted separately andtangentially to the spiral turns. Thus it is possible to adjust theouter edge of the synchronizing margin strip separately for the twoareas B and A so that the synchronizing 5 impulses are generated atexactly equal intervals. The position of the two diaphragms 6 and I isdrawn for rectangular image areas. In the case of trapezoidal areas theinner edges of the diaphragm should be positioned radially. 10

I claim:

In television apparatus for interlaced scanning, a scanning disc havingpositioned thereon a plurality of elemental scanning openings arrangedabout the outer area of the disc in spiral forma- 15 tion to form twocomplete spiral turns, each of said spiral turns having a pitchsubstantially equal to the height of an image area to be scanned and theseparation of the individual elemental scanning openings on each spiralhaving 20 substantially an equal angular spacing one from the other anda linear spacing along the spiral path varying in accordance with theradial spacing from the disc center, so that an image pattern ofpredetermined configuration is scanned, said disc being adapted to beilluminated with a band of light of substantially fixed intensity alonga strip adjacent a radial edge of the said image pattern area, thecombination of two light masking elements each having one edge coincidewith a radial edge of the pattern scanned by the disc and located in thepath of the fixed intensity light, and each masking element beingassociated with one of the spiral paths only and adapted to be movedtangentially relatively to its associated spiral path to vary therebythe radial position at which the fixed intensity light is revealed tothe disc so that substantially identical areas are scanned by eachspiral turn .of the scanning element.

KURT SCHLESINGER.

